How can I override this method in this interface (see code)?

Question

I have an interface called A:

public interface A { 
    void X(T t);
}

I then have two subclasses (B and C) that implement this interface, but each of them pass a different type to X lets say B passes type foo and C passes type bar:

public class B implements A {
    @Override
    public <T extends foo> void X(T type1)
}

public class C implements A {
    @Override
    public <T extends bar> void X(T type2)
}

What am I doing wrong and why doesn't this work? The compiler keeps telling me that "Method does not override method from its superclass".

Thanks in advance!

Answer 1

Even with generic methods, when they are overridden, the generics must match exactly.

One way that might not meet your requirements is to remove the upper bounds on the implementing class, e.g.

class B implements A {
    @Override
    <T> void X(T type1) { /* impl */ }
}

But if you need the upper bound, then represent the upper bound with a type parameter on the interface.

interface A<U> { 
    <T extends U> void X(T t);
}

Then you can supply the type argument for the upper bound in the implementing classes.

class B implements A<Foo> {
    @Override
    public <T extends Foo> void X(T type1) { /* impl */ }
}

class C implements A<Bar> {
    @Override
    public <T extends Bar> void X(T type2) { /* impl */ }
}

But because anything you can call on T you can also call on Foo or Bar, maybe the methods don't need to be generic.

interface A<T> { 
    void X(T t);
}
class B implements A<Foo> {
    @Override
    public void X(Foo type1) { /* impl */ }
}

class C implements A<Bar> {
    @Override
    public void X(Bar type2) { /* impl */ }
}